Process for the treatment of bismuth foam obtained in the refining of bi-containing lead



United States Patent PROCESS FDR THE TREATMENT OF BISMUTH FOAM OBTAINED IN THE REFINING OF Bi- CONTAINING LEAD Gerhard Werner, Hamburg, Germany, assignor to Norddeutsche Atfinerie, Hamburg, Germany No Drawing. Application July 18, 1955, Serial No. 522,859

Claims priority, application Germany October 25, 1954 4 Claims. (Cl. 75-70) The present invention relates to an improved process for working up bismuth foams obtained in the refining of bismuth containing lead with alkali, alkaline earth and earth metals in order to recover values from such foams.

it is already known that the bismuth foams obtained in refining bismuth containing lead can be worked up by a treatment with chlorine or by fusion under salt fluxes. In the latter procedure it is for example recommended that the foams obtained by refining bismuth containing lead with Ca and Mg be liquated under a cover of CaClz and NaCl whereby a bismuth containing liquation-lead is obtained, which is recycled, and a foam is obtained from which a lead bismuth alloy can be recovered after removal of Ca and Mg, which alloy is to be worked up by treatment with chlorine or by electrolysis. It is also known to work up bismuth foams or the lead bismuth alloys obtained in the above mentioned liquation procednre to remove Ca and Mg by fusion with ZnCl2CaCl2 or PbClz slags during which the Ca and Mg contained in the foam or alloy goes over into the slag in exchange for Zn and Pb.

The object of the present invention is to provide a new and improved process using simple and easily available materials to convert the alkali, alkaline earth and earth metal content of bismuth foams into a relatively small quantity of chloride containing dross and to obtain a lead-bismuth alloy which contains at least 95% of the bismuth contained in the foam and can be directly cast to form anodes for electrolytic refining.

According to the invention it was found that the bismuth foam which cannot or hardly can be melted down without a salt cover can be decomposed into a lead bismuth alloy free of alkali, alkaline earth and earth metals and to a chloridic dross which ultimately becomes lumpy by treating such foam after heating to over 500 C., preferably to 550 to 600 C., with hydrochloric acid. Preferably the hydrochloric acid is added slowly and the treated material is stirred vigorously. The addition of hydrochloric acid is interrupted as soon as the dross is converted from a powdery state to a lumpy state. During the addition of the hydrochloric acid an evolution of hydrogen occurs which can be recognized by the small flames produced. The hydrogen effects an advantageous reduction of lead and bismuth. The whole procedure is exothermic and causes some rise in temperature. When the treatment is carried out with vigorous stirring the alloy which melts out separates out from the dross fioating thereon which is first powdery and then becomes lumpy. The dross obtained is about 57% of the weight of the bismuth foam treated. The alloy which melts out is free of alkali, alkaline earth and earth metals. An investigation of the chloride containing drosses obtained indicates that complete conversion of the Ca and Mg, which may for example be present, to the corresponding chlorides is not necessary in order to obtain successful segregation of such metals in the dross. To the contrary it was found that a quantity of hydrochloric acid which is only sufficient to convert /a to /2 of the Ca 2,751,290 Patented June 19, 1956 and Mg as well as any other alkali, alkaline earth and earth metalscontained in the bismuth foam suflices.

It was furthermore found that the hydrochloric acid treatment could be shortened and that the quantity of 5 hydrochloric acid required could be reduced by about 30% 'when the bismuth foam was poled with steam of, for example, about 3 atmospheres gauge pressure at about 600 C. before the hydrochloric acid treatment. This 'procedure which is known per se also is exothermic and causes a rise in temperature. It causes oxidationof the alkali, alkaline earth and earth metals as well as a partial oxidation of the lead and bismuth. In addition thereto it causes physical changes in the foams in which a considerable quantity of the lead and bismuth separate out as an alloy. The refining effect of the steam poling, however, is limited in that a quantity of dross is produced which is about 30% of the foam treated and in that residues of Ca and Mg remain in the bismuth lead alloy which can amount to about 0.02% of each of these metals. The advantages of the pretreatment by poling with steam resides in the above-mentioned saving in time and hydrochloric acid in the subsequent hydrochloric acid treatment as the pretreated material which is to be treated with hydrochloric acid essentially comprises the dross produced by the poling treatment which is not only quantitatively smaller than the original bismuth foam but also is more reactive to the hydrochloric acid treatment.

When the foams which have been poled with steam are subsequently treated with hydrochloric acid in accordance with the invention the alkali, alkaline earth and earth metals still retained in the lead bismuth alloy are quickly and completely removed and the dross resulting from the poling treatment is converted to such an extent that only 5 to 6% of chloridic dross remains. When the hydrochloric acid treatment is effected upon the foams pretreated by poling with steam, no essential rise in temperature occurs.

The following example will serve to illustrate the process according to the invention:

Example 3.3 tons of bismuth foam heated to about 600 C. were poled with steam at about 3 atmospheres gauge pressure until the dross produced amounted to about 30% of the original foam. Then 63.5 kg. of hydrochloric acid (33% HCl) were gradually added to the pretreated product with stirring at temperatures between 550 and 600 C. Upon completion of the addition of the hydrochloric acid the dross had been converted from a powdery state to a lumpy state. The weight of the dross produced was 0.175 ton and the weight of the lead bismuth alloy produced was 3.14 tons. The lead-bismuth alloy contained 95.4% Pb and 4.6% Bi and it was cast to form anodes for electrolytic refining. The dross contained 41.5% Pb, 2.4% Bi, 9.9% Ca, 13.1% Mg and 13.4% Cl. Consequently, 97.6% of the lead in the bismuth foam treated was recovered in the lead-bismuth alloy and only 2.4% were retained in the dross. A similar distribution of the bismuth also occurred as 97.2% were recovered in the lead bismuth alloy and 2.8% in the dross. Including the pre-poling, two hours were required for the treatment of the charge. The dross was recycled to the shaft furnace employed for the lead metallurgy.

Similar results were obtained when the bismuth foam was directly subjected to the hydrochloric acid treatment without pre-poling with steam except that about more hydrochloric acid was required before the dross had assumed a lumpy state.

I claim:

1. A process for the treatment of bismuth foam obtained in the refining of bismuth containing lead with at least one metal selected from the group consisting of tr alkali, alkaline earth and earth metals, which comprises treating such foam with hydrochloric acid at a temperature above 500 C.

2. A process according to claim 1 in which the quantity of hydrochloric acid employed for the treatment is only /a to /2 that required to chloridize any alkali, alkaline earth and earth metal contained in the foam.

I 3. A process for the treatment of bismuth foam obtained in the refining of bismuth containing lead with at least one metal selected from the group consisting of alkali, alkaline earth and earth metals, which comprises slowly adding hydrochloric acid to said foam heated to a temperature between 550 and 600 C. while stirring until the dross formed becomes lumpy.

4. A process for the treatment of bismuth foam obtained in the refining of bismuth containing lead with at least one metal selected from the group consisting of alkali, alkaline earth and earth metals, which comprises poling said foam which has been heated to about 600 C. with steam, and subsequently slowly adding hydrochloric acid to the poled product heated to a temperature above 500 C. While stirring until the dross formed becomes lumpy;

No references cited. 

1. A PROCESS FOR THE TREATMENT OF BISMUTH FOAM OBTAINED IN THE REFINING OF BISMUTH CONTAINING LEAD WITH AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF ALKALI, ALKALINE EARTH AND EARTH METALS, WHICH COMPRISES TREATING SUCH FOAM WITH HYDROCHLORIC ACID AT A TEMPERATURE ABOVE 500* C. 